Hydrogen is commonly supplied to customers that are connected to a supplier's hydrogen pipeline system. Typically, the hydrogen is manufactured by steam methane reforming in which a hydrocarbon such as methane and steam are reacted at high temperature in order to produce a synthesis gas containing hydrogen and carbon monoxide. Hydrogen may then be separated from the synthesis gas to produce a hydrogen product stream that is introduced into the pipeline system for distribution to customers that are connected to the pipeline system. Alternatively, hydrogen produced from the partial oxidation of a hydrocarbon can be recovered from a hydrogen rich stream.
Typically, hydrogen is supplied to customers under agreements that require availability and reliability for the steam methane reformer or hydrogen recovery plant. When a steam methane reformer is taken off-line for unplanned or extended maintenance, the result could be a violation of such agreements. Additionally, there are instances in which customer demand can exceed hydrogen production capacity of existing plants in the short term. Having a storage facility to supply back-up hydrogen to the pipeline supply is therefore desirable in connection with hydrogen pipeline operations.
Considering that hydrogen production plants on average have production capacities that are roughly 50 million standard cubic feet per day, a storage facility for hydrogen that would allow a plant to be taken off-line, to be effective, would need to have storage capacity in the order of 1 billion standard cubic feet or greater.
In order to provide this large storage capacity, high pressure gases, such as but not limited to nitrogen, air, carbon dioxide, hydrogen, helium, and argon, are stored in caverns, whether leached in salt formations or created by hard rock mining. A minimum volume of gas is stored in the cavern to provide adequate pressure to maintain the integrity of the cavern and prevent the cavern roof from collapsing and to keep the cavern walls from moving inward. This minimum volume of gas is called the pad gas or base gas. The amount of gas stored in addition to the pad gas or base gas volume is called the working gas or working inventory. Business opportunities can require removing more gas volume from the cavern than the working gas volume. To meet this business need, the volume of pad gas or base gas can be reduced to provide additional volume. For the purpose of this invention, the definition of high pressure is defined as a pressure at or above 10 atm. For the purpose of this invention, the definition of cavern integrity is defined as the ability of the cavern to hold static pressure when blocked in for 48 hours such that the cavern gas pressure does not decrease for 48 hours when all flows in and out of the cavern are stopped.